Pipe metal and welded connection defect repair by cladding

Cladding repair is the one of the most simple and least expensive repair technologies. It refers to both permanent and temporary repair methods. It reduces work costs and time of repair works while retaining the quality required by the statutory requirements. With the help of cladding repair, a significant number of defects of corrosion-mechanical origin can be eliminated. The problem of improving this technology is of utmost importance. The purpose of the present research is to develop the technology for effective and safe cladding repair of such defects as corrosion damages of pipe metal and such welded connection defects as incomplete groove filling, undercut, pores, strikes, slag inclusion. The following problems were solved to reach this goal: research of thermal cycles in the course of cladding, research of cladding modes, development of multipass repair technology, determination of allowable defect parameters, and detection of methods for optimal quality control of repaired areas. The specialists performed testing of full-scale pipe samples and circular joint of pipes, imitating the surface defects after cladding repair. The test results did not reveal the damage of metal and welded connection areas. Cladding repair allows recovering bearing capacity of pipeline to design level. This technology can be used in the works on shutdown pipelines and on pipelines under operation.

The Conjugative Transposon Tn5397 Has a Strong Preference for Integration into Its Clostridium difficile Target Site

ABSTRACT Tn5397 is a conjugative transposon, originally isolated from Clostridium difficile. The Tn5397 transposase TndX is related to the phage-encoded serine integrases and the Clostridium perfringens Tn4451 transposase TnpX. TndX is required for the insertion and excision of the transposon. Tn5397 inserts at one locus, attBCd , in C. difficile but at multiple sites in Bacillus subtilis. Apart from a conserved 5′ GA dinucleotide at the recombination site, there appears to be little sequence conservation between the known target sites. To test the target site preference of Tn5397, attBCd was introduced into the B. subtilis genome. When Tn5397 was transferred into this strain, 100% of the 50 independent transconjugants tested had Tn5397 inserted into attBCd . This experiment was repeated using a 50-bp attBCd with no loss of target preference. The mutation of the 5′ GA to 5′ TC in the attBCd target site caused a switch in the polarity of insertion of Tn5397, which is consistent with this dinucleotide being at the crossover site and in keeping with the mechanism of other serine recombinases. Tn5397 could also transpose into 50-bp sequences encoding the end joints attL and attR but, surprisingly, could not recombine into the circular joint of Tn5397, attTn. Purified TndX was shown to bind specifically to 50-bp attBCd , attL, attR, attTn, and attBBs 3 with relative binding affinities attTn ≈ attR > attL > attBCd > attBBs 3. We conclude that TndX has a strong preference for attBCd over other potential recombination sites in the B. subtilis genome and therefore behaves as a site-specific recombinase.